The invention relates generally to knives with changeable blades and more particularly such knives used by carpet layers which include a handle and blade holder for demountably securing a heavy-duty, razor-style blade having two sharpened edges and an open center section for mounting the blade in the handle.
Carpet layers use a knife of this character for cutting and trimming during carpet installation. The carpet to be cut sometimes is heavy, necessitating a sharp blade and good leverage to cut along a precise outline. A substantial amount of cutting and trimming must be done even in carpeting a small room. Consequently, though heavy-duty blades are used, the blades quickly become dull and must be changed. In order to always have a sharp knife, a carpet layer should use about 15 blades in the course of a day's work.
The customary handle and blade holder has two half sections formed to receive and clamp the blade therebetween. The blade holder must be capable of holding the blade firmly against both longitudinal forces which tend to push the blade into the handle and torques which tend to rotate the blade. In many knives the screw that holds the sections together passes through the open center portion of the blade to apply the maximum compressive force to hold the blade tightly between the sections. In other knives of the prior art the blade is held firmly in position by projections extending through the open center of the blade or by in-turned flanges holding the edges of the blade. Though such blade-holding arrangements adequately secure the blade in position, they require complete removal of the clamping screw and disassembly of the knife half sections in order to change blades or to reverse the blade to expose a different edge, and then the sections must be reassembled. The process of disassembly and reassembly frequently even requires the use of a screw driver. The need to disassemble the knife to change or reverse the blade is inconvenient and time consuming. The effort and time loss involved in changing blades causes carpet layers to use blades beyond their sharp condition which further reduces working efficiency.
A serious problem in using known knives is the hazard presented by exposure to the extremely sharp blades. Spare blades are usually stored in a compartment formed in the handle sections of knives. Disassembly of the sections to change or reverse the blade necessarily opens the storage compartment, and the blades frequently spill from the storage compartment, exposing the sharp edges. Accidental injury due to handling of the blades is not uncommon in the carpet laying trade.